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DOI: 10.1055/s-2003-41410
Synthesis of Long Chain 2-Alkyl-1-(2-hydroxyethyl)-2-imidazolines under Microwave in Solvent-Free Conditions
Publication History
Publication Date:
28 August 2003 (online)
Abstract
An efficient method for the synthesis of long chain 2-alkyl-1-(2-hydroxyethyl)-2-imidazolines, and their amide precursors, by condensing aminoethylethanolamine and several fatty acids under non-solvent microwave irradiation using CaO as support, is described. Products were obtained in good yields and high purity in a few minutes, in both multimode microwave and monomode microwave oven. Evidences of non-thermal microwave effects are given.
Key words
microwave - solid-phase synthesis - cyclizations - imidazolines - amides
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References
For microwave safety consideration see ref. [5a] , p. 175-179.
9Microwave irradiations was carried out with a DMW (Panasonic NM-5460A, 800 W, 2450 MHz) and a MMW (MIC-I, 600 W, from SEV, México). For the reactions using a DMW the final temperatures were measured directly, immediately at the end of the reaction, with a contact thermometer embedded in the reaction mixture. For a comparison multimode vs monomode microwave oven see ref. [4b] and ref. [6a]
10Typical Experimental Procedure: In an open Pyrex vessel (100 mL, for DMW) or sealed tube (100 mL, for MMW) were carefully mixed 0.52 g (5.0 mmol) of aminoethyl-ethanolamine (3), 5.0 mmol of the corresponding fatty acid (4a-d) and 2.5 g of CaO. The resulting mixture was irradiated using the power and the reaction time showed in Table [1] . The reaction mixture was allowed to reach room temperature, EtOAc (20 mL) was added and the mixture was heated until boiling and filtered off while hot, and the filtrated was concentrated under vacuum to dryness, yielding the corresponding product as a white solid.
11
[2-(2-Hydroxyethylamino)ethyl]heptadecylamide (2a): Recrystallization from EtOAc. Mp 102-103 °C (lit
[3a]
103-105 °C). IR (KBr): 3300-3270, 2920, 2850, 1641 cm-1. 1H NMR (200 MHz, CDCl3): δ = 0.86 (t, J = 6.0 Hz, 3 H), 1.23 (sa, 28 H), 1.45-1.63 (m, 2 H), 2.19 (t, J = 7.9 Hz, 2 H), 2.72-2.92 (m, 4 H), 3.39 (q, J = 6.0 Hz, 2 H), 3.70 (t, J = 5.0 Hz, 2 H), 4.10 (sa, 1 H). 13C NMR (50 MHz, CDCl3): δ = 14.3, 22.8, 26.0, 29.4, 29.6, 29.7, 32.0, 36.8, 38.9, 48.6, 51.1, 60.4, 173.5.
2-Heptadecyl-1-(2-hydroxyethyl)-2-imidazoline (1a): Recrystallization from EtOAc. Mp 62-63 °C (lit
[3a]
63-65 °C). IR (KBr): 3310, 2917, 2849, 1602 cm-1 1H NMR (200 MHz, CDCl3): δ = 0.86 (t, J = 6.0 Hz, 3 H), 1.23 (sa, 28 H), 1.45-1.65 (m, 2 H), 2.22 (t, J = 5.8 Hz, 2 H), 3.22 (t, J = 5.4 Hz, 2 H), 3.29-3.39 (m, 2 H), 3.61-3.71 (m, 4 H), 3.76 (sa, 1 H). 13C NMR (50 MHz, CDCl3): δ = 14.3, 22.8, 26.6, 28.0, 29.5, 29.68, 29.72, 29.8, 49.4, 50.2, 51.6, 59.8, 168.0.
The thermal heating reaction protocol was as in the case of microwave methodology except that the glass tube containing the reagents and a magnetic stirring bar, was placed into a preheated oil bath at 150 ºC. The temperature of each was measured for 5 s using a thermometer embedded in the reaction mixture. The work-up procedure was as with the microwave methodology.